The technical field of the invention is that of needleless syringes used for subdermal or intramuscular injection of various active principles in pulverulent form for therapeutic use in human or veterinary medicine.
More specifically, the invention relates to a needleless syringe using a gas generator which is intended to create a pressure wave for ejecting the particles of active principle. A burstable inner seal, placed on the pathway of the gases, makes it possible to obtain the threshold pressure level permitting ejection of the particles at a sufficiently high speed. This is because the sudden release of the gases creates a shock wave in the syringe and it is this shock which will carry and accelerate the particles in order to expel them. The specificity of the invention lies in the fact that the inner seal has another function than that of contributing to creating a shock wave: it also serves as a system for retention of the solid particles of active principle.
Needleless syringes which function by generating a shock for entraining the solid particles of active principle already exist and have been the subject of several patents. Mention may be made, in particular, of patent WO 94/24263 which describes a needleless syringe functioning by release of a reserve of gas in order to entrain the solid particles of active principle. In said patent, one of the main characteristics is that the particles are maintained permanently on the pathway of the gases, between two burstable membranes.
Other patents concerning devices other than needleless syringes describe mechanisms for ejection of solid particles. Mention may be made, for example, of patent U.S. Pat. No. 5,478,744 which concerns a device with which it is possible to bombard cell cultures with inert or biologically active particles, and whose operating principle is based on the release of a compressed gas in a tube which can be supplied with particles from the side. This same patent describes a mechanism for ejection of solid particles involving a weight which carries said particles, is accelerated under the action of the compressed gases, and is then suddenly stopped by a limit stop, allowing the particles to continue their course at high speed.
Neither of the two patents mentioned above relates to mechanisms for ejection of solid particles involving an inner seal with the double function of carrying the particles and of creating a shock wave.
The needleless syringe according to the invention is able to eject solid particles of active principle under the effect of a shock wave produced by the release of a compressed gas.
Using a pyrotechnic charge makes it possible to satisfy the double requirement of performance and reliability. This is because a powder charge can produce a large quantity of gas in a very short time and thus contribute to generating a shock wave, the speed of whose front can be very high. Consequently, the particles of active principle undergo substantial acceleration, promoting their penetrating ability, while the blast at the syringe exit dissipates very rapidly into the ambient air. In addition, the firing of miniaturized pyrotechnic charges is perfectly controlled by means of initiators which have been widely tried and tested and adapted to the characteristics of said charges to be initiated, thereby making the needleless syringes according to the invention very reliable. Finally, by using an inner seal which has the double function of containing the particles of active principle and of creating a shock wave, it is possible to reduce the size of the syringe and to simplify the operating mechanism by reducing the number of parts involved.
The subject of the present invention is a needleless syringe comprising, in succession, a gas generator, a gas expansion chamber, a means for retention of the particles of active principle, and a tube for ejection of said particles, characterized in that the means for retention of the particles is formed by an inner seal which has at least one cavity intended to house the particles, said inner seal being designed to burst at the level of this cavity when it is subjected to a threshold pressure level. The inner seal preferably has, at the level of this cavity, at least one line of weakening which is designed to promote its opening upon release of the particles. According to a preferred embodiment of the invention, the inner seal is formed by at least two symmetrical elements attached along a line of opening which permits release of the particles. One of the objects intended to be achieved by this type of configuration is a clean breaking of the inner seal in order to properly release the solid particles of active principle without production of parasite particles which may originate from the inner seal and be expelled. Moreover, since the particles of active principle are to be released just before the creation of the shock wave in the tube, or at the latest at the same time, it is therefore desirable to promote rupturing of the inner seal at the level of the cavity containing the particles of active principle. The inner seal advantageously has a transverse position in relation to the axis of the ejection tube and has, on its downstream face, a central extension in which the cavity is situated.
According to a first preferred embodiment of the invention, the inner seal is fixed and comprises a closed cavity at its center. For this configuration, the inner seal marks the boundary between the expansion chamber and the ejection tube. In this way, when the pressure in the expansion chamber reaches a threshold value, the inner seal opens at the level of its cavity, permitting release of the particles of active principle into the ejection tube and almost simultaneously provoking the creation of a shock wave in said tube.
According to a second preferred embodiment of the invention, the inner seal constitutes one of the two ends of a hollow cylinder situated in the expansion chamber. More precisely, the outer lateral wall of the hollow cylinder is in contact with the inner lateral wall of the chamber, and the inner seal is situated at that end of the cylinder farthest from the gas generator. The cavity of the inner seal is advantageously blind and is obturated by a transverse membrane fixed in the ejection tube. The transverse membrane is preferably fixed at the level of an internal shoulder marking the limit between the chamber and the ejection tube, and the hollow cylinder is held in the chamber by virtue of the membrane with which it is in contact. The inner seal is advantageously bonded to the transverse membrane. The gases emitted by the gas generator preferably cause the displacement of the hollow cylinder as far as the internal shoulder against which it abuts, this displacement entailing the rupturing of the membrane by the central extension of the innner seal as it passes through, and also immediately causing the release of the solid particles of active principle. The membrane advantageously has a small thickness and is formed by a nonelastic material. The membrane has a double function: it obturates the cavity in order to maintain the particles in their seat and also serves as a fixation surface for the hollow cylinder. The edge of the blind cavity is preferably tapered to facilitate the opening of the membrane, said membrane being pre-cut radially as far as the center in order to promote opening in the manner of petals. This membrane must be dimensioned in such a way that it does not impede the displacement of the hollow cylinder by offering too much resistance, and in such a way that it does not divide into several pieces at the moment it ruptures. According to this second preferred embodiment of the invention, the gases emitted initially provoke the displacement of the hollow cylinder, which tears the membrane and permits the release of the particles of active principle into the ejection tube. The cylinder is subsequently blocked against the internal shoulder and, when the pressure of the gases reaches a threshold value in the space between the gas generator and the inner seal, said inner seal opens, creating a shock wave.
The inner seal is advantageously calibrated to yield at a pressure of at least 20 bar, but this pressure of rupture must be adapted depending on the granulometry and the density of the particles of active principle, in such a way that the speed of ejection of the particles at the outlet of the ejection tube is greater than 750 meters per second.
According to another embodiment of the invention, the inner seal has several cavities aligned in the same direction. The inner seal preferably has a rectilinear line of weakening passing through all the cavities. By this means, all the cavities open concomitantly, permitting creation of a single intense shock wave.
The gas generator is advantageously a pyrotechnic gas generator comprising a pyrotechnic charge and a device for initiation of said charge.
The initiation device preferably comprises a percussion system and a primer currently used in the pyrotechnics industry. However, it is also possible to initiate the pyrotechnic charge by other means, and in particular those involving either a piezoelectric crystal or a roughened area or even a battery. The trigger is advantageously situated at one of the ends of the syringe in the form of a push button in order to make it easier to grip and operate.
The needleless syringes according to the invention benefit from the advantages associated with functioning by means of a shock wave, in particular in terms of the speed of ejection of the particles, while at the same time ensuring reliable maintenance of the particles in storage mode.
Moreover, the use of an inner seal having the double function of housing the particles of active principle and of creating a shock wave makes it possible to simplify the operating mechanism of the syringe by limiting the number of parts involved.
Finally, maintaining the particles in the pathway of the gases is a guarantee that all the particles of active principle will be in a position to be accelerated by the shock wave.